Patterned strained semiconductor substrate and device

ABSTRACT

A device that includes a pattern of strained material and relaxed material on a substrate, a strained device in the strained material, and a non-strained device in the relaxed material. The strained material may be silicon (Si) in either a tensile or compressive state, and the relaxed material is Si in a normal state. A buffer layer of silicon germanium (SiGe), silicon carbon (SiC), or similar material is formed on the substrate and has a lattice constant/structure mis-match with the substrate. A relaxed layer of SiGe, SiC, or similar material is formed on the buffer layer and places the strained material in the tensile or compressive state. Carbon-doped silicon or germanium-doped silicon may be used to form the strained material. The structure includes a multi-layered substrate having strained and non-strained materials patterned thereon.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/931,836, filed Oct. 31, 2007, which is a divisional of U.S. patentapplication Ser. No. 10/710,608, filed Jul. 23, 2004, now U.S. Pat. No.7,384,829, the disclosures of which are expressly incorporated byreference herein in their entirety.

BACKGROUND OF INVENTION

1. Field of the Invention

The invention relates to methods and structures for manufacturingsemiconductor devices having improved device performances, and moreparticularly, to methods and structures for forming patterns of strainedand non-strained areas on a substrate.

2. Background Description

Emerging technologies, such as embedded Dynamic Random Access Memory(eDRAM), Application Specific Integrated Circuits (ASIC), andsystem-on-chip (SoC), require the combination of high-performance logicdevices and memory devices on the same chip. It is also desired to havedigital circuits and analog circuits on the same chip for someapplications. It has been shown that logic devices exhibit betterperformance when formed on a tensily strained silicon layer that isepitaxially grown on another epitaxially grown silicon germanium (SiGe)layer that has been relaxed.

A fully relaxed SiGe layer has a lattice constant which is larger thanthat of silicon. Thus, when the silicon layer is epitaxially grownthereon, the silicon layer conforms to the larger lattice constant ofthe relaxed SiGe layer and this applies physical biaxial stress to thesilicon layer being formed thereon. This physical biaxial stress appliedto the silicon layer increases the performance of logic devices formedin the strained silicon.

Relaxation in SiGe on silicon substrates occurs through the formation ofmisfit dislocations, which when equally spaced to relieve stress causethe substrate to be perfectly relaxed. Additionally, the misfitdislocations provide extra half-planes of silicon in the substrate. Thisallows the lattice constant in the SiGe layer to seek its intrinsicvalue. In this manner, the SiGe lattice constant grows larger as themismatch strain across the SiGe/silicon interface is accommodated.

The problem with this approach is that it requires a very thick,multilayered SiGe layer. Additionally, the misfit dis-locations formedbetween the SiGe layer and the epitaxial silicon layer are random,highly non-uniform in density, and fairly uncontrollable due toheterogeneous nucleation that cannot be easily controlled. Consequently,the physical stress applied to the silicon layer is apt to be defective.At locations where misfit density is high, defects form in the strainedsilicon layer. These defects short device terminals and cause otherleakage problems. For this reason, although the performance of logicdevices is strengthened when the logic devices are formed in areas ofstrained silicon, the performance of defect-sensitive devices such asDRAM devices degrades when formed therein. The production yield is alsocompromised when the defect-sensitive devices are formed in the strainedregions. Thus a need exists for a method of (and a substrate for)manufacturing strained and non-strained silicon regions on the same chipso that high-performance logic devices can be made in the strainedsilicon regions and high quality, defect-sensitive devices can be madein the non-strained regions.

SUMMARY OF INVENTION

In one aspect of the invention, a method for forming an electricaldevice is provided. The method includes forming a pattern of strainedmaterial and non-strained (relaxed) material on a substrate. The methodfurther includes forming a strained device in the strained material. Themethod yet further includes forming a non-strained device in thenon-strained material.

In another aspect of the invention, another method for forming anelectrical device is provided. The method includes forming a bufferlayer in contact with a portion of a substrate. The buffer layer has alattice constant/structure mismatch with the substrate. The method alsoincludes forming a relaxed layer on the buffer layer. The method furtherincludes forming a strained material on a top surface of the relaxedlayer. The relaxed layer places the strained material in one of atensile or a compressive state. The method yet further includespatterning a non-strained (relaxed) material proximate the strainedmaterial.

In still another aspect of the invention, an electrical device isprovided. The device includes a substrate. The device further includes apattern of strained material and relaxed material formed on thesubstrate. The device yet further includes a strained device formed inthe strained material. The device still further includes a non-straineddevice formed in the relaxed material.

In yet another aspect of the invention, another electrical device isprovided. The electrical device includes a buffer layer formed incontact with a portion of a substrate. The buffer layer has a latticeconstant/structure mismatch with the substrate. The device furtherincludes a relaxed layer formed on the buffer layer. The device alsoincludes a strained material formed on a top surface of the relaxedlayer. The relaxed layer places the strained material in one of atensile or a compressive state. The device still further includes anon-strained material patterned proximate the strained material.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1-4 show fabricating steps of manufacturing an electrical deviceaccording to a first embodiment of the invention;

FIG. 5 shows a final structure of an electrical device according to afirst embodiment of the invention;

FIGS. 6-10 show fabricating steps of manufacturing an electrical deviceaccording to a second embodiment of the invention;

FIG. 11 shows a final structure of an electrical device according to asecond embodiment of the invention;

FIGS. 12-15 show fabricating steps of manufacturing an electrical deviceaccording to a third embodiment of the invention;

FIG. 16 shows a final structure of an electrical device according to athird embodiment of the invention;

FIGS. 17-21 show fabricating steps of manufacturing an electrical deviceaccording to a fourth embodiment of the invention;

FIG. 22 shows a final structure of an electrical device according to afourth embodiment of the invention;

FIGS. 23-26 show fabricating steps of manufacturing an electrical deviceaccording to a fifth embodiment of the invention;

FIG. 27 shows a final structure of an electrical device according to afifth embodiment of the invention;

FIGS. 28-31 show fabricating steps of manufacturing an electrical deviceaccording to a sixth embodiment of the invention;

FIG. 32 shows a final structure of an electrical device according to asixth embodiment of the invention;

FIG. 33 is a cross-sectional view of an electrical device according to aseventh embodiment of the invention that is formed using a combinationof the methods and materials shown in FIGS. 1-32;

FIG. 34 is a flowchart representing fabricating steps of manufacturingthe electrical device shown in FIGS. 1-5;

FIG. 35 is a flowchart representing fabricating steps of manufacturingthe electrical device shown in FIGS. 6-11;

FIG. 36 is a flowchart representing fabricating steps of manufacturingthe electrical device shown in FIGS. 12-16;

FIG. 37 is a flowchart representing fabricating steps of manufacturingthe electrical device shown in FIGS. 17-22;

FIG. 38 is a flowchart representing fabricating steps of manufacturingthe electrical device shown in FIGS. 23-27; and

FIG. 39 is a flowchart representing fabricating steps of manufacturingthe electrical device shown in FIGS. 28-32.

DETAILED DESCRIPTION

The invention is directed to an electrical, digital, semiconductor, orother device having a substrate on which a pattern of strained andnon-strained (i.e., relaxed) materials are formed. The strained materialmay be placed in tension or compression due to a latticeconstant/structure difference with an underlying layer of relaxedmaterial. In turn, the relaxed material is formed on a buffer layer,which contacts a portion of the substrate.

A material forming the buffer layer varies in concentration throughoutthe layer, and has a lattice constant/structure mismatch with thematerial that forms the substrate. Because the material forming thebuffer layer increases in concentration the further the buffer layerextends from the substrate, defects normally caused by the latticemis-match are virtually eliminated. The formation of the relaxed layeron the buffer layer further reduces and/or eliminates defects to such anextent that the strained material is virtually free of defects. Thedrastic reduction or elimination of defects in the strained materialallows electronic or digital devices formed therein to operate very fastand very efficiently. It also allows devices such as Dynamic RandomAccess Memory (DRAM) to be formed in an adjacent relaxed materialbecause such devices are normally very sensitive to defects. Thus,embodiments of the invention permit the forming of strained logicdevices and non-strained memory devices side by side on the samesubstrate.

Referring now to FIGS. 1-5, there is shown a cross-section of a portionof an electrical device 100. “Electrical device” refers to anelectrical, electro-mechanical, semiconductor, digital, or similardevice. Illustrative types of electrical devices include, but are notlimited to, transistors, capacitors, resistors, logic devices, memorydevices, computer processors, traces, vias, semi-conductor wafer,computer chip, application specific integrated circuit (ASIC),system-on-chip (SoC), and the like. As shown in FIG. 1, the electricaldevice 100 includes a substrate 101 covered with a pad layer 103.

The substrate 101 is formed of any suitable material, for example,silicon (Si). Other suitable alternative types of substrates includegermanium (Ge), silicon germanium (SiGe), silicon carbide (SiC), andthose consisting essentially of one or more compound semiconductorshaving a composition defined by the formulaAl_(X1)Ga_(X2)In_(X3)As_(Y1)P_(Y2)N_(Y3)Sb_(Y4), where X1, X2, X3, Y1,Y2, Y3, and Y4 represent relative proportions, each greater than orequal to zero and X1+X2+X3+Y1+Y2+Y3+Y4=1 (1 being the total relativemole quantity). Other suitable substrates have a composition Zn_(A1)Cd_(A2) Se_(B1) Te_(B2), where A1, A2, B1, and B2 are relativeproportions each greater than or equal to zero and A1+A2+B1+B2=1 (1being a total mole quantity). Alternatively, the substrate has asemiconductor-on-insulator type structure, e.g., a silicon-on-insulator(SOI) substrate. In one embodiment, the thickness of the substrateapproximates that of a standard semiconductor wafer known in the art.

The pad layer 103 acts to prevent the layers which are directly beneathit from being removed by any of the subsequent processes. By selectivelypatterning openings in the pad layer, recesses can be formed through allor portions of the underlying substrate layers, as discussed below.Additionally, use of the pad layer permits the epitaxial growth (anddeposition) of specific materials such as Si, Ge, SiGe, SiC, thoseconsisting essentially of one or more compound semiconductors having acomposition defined by the formulaAl_(X1)Ga_(X2)In_(X3)As_(Y1)P_(Y2)N_(Y3)Sb_(Y4), where X1, X2, X3, Y1,Y2, Y3, and Y4 represent relative proportions, each greater than orequal to zero and X1+X2+X3+Y1+Y2+Y3+Y4=1 (1 being the total relativemole quantity), and those having a compositionZn_(A1)Cd_(A2)Se_(B1)Te_(B2), where A1, A2, B1, and B2 are relativeproportions each greater than or equal to zero and A1+A2+B1+B2=1 (1being a total mole quantity). Each of these exemplary materials may beapplied to all embodiments described herein.

The material forming the pad layer 103 will vary depending on the typeof manufacturing process used. Exemplary pad layer materials include,but are not limited to, silicon nitride and/or silicon oxide. Personsskilled in the art, however, will readily understand additional types ofmaterials that can be used to form the pad layer. Illustratively, thepad layer has an overall thickness of about 0.2 microns when it isdesired to form a recess that is approximately 2.0 micron deep. Thisexemplary thickness may be applied to all embodiments herein described.

In FIG. 2, the substrate 101 is shown having a recess 105 formed thereinformed using reactive ion etching or dry etching processes. The exactwidth of recess 105 is not critical, but the depth is formed in therange of about 1.0 micron to about 3.0 microns deep. An exemplary widthis about 100 microns. These illustrative recess measurements may beapplied to all embodiments disclosed herein. Thereafter, an insulatinglayer 107 formed of an oxide or nitride material is conformallydeposited on the sidewalls and bottom 109 of the recess 105 using anysuitable deposition or growth process known in the art. Illustratively,the insulating layer is formed to be in the range of approximately 10Angstroms to about 100 Angstroms thick. This exemplary measurement maybe applied to all embodiments described herein. After the insulatinglayer 107 is formed, lateral, but not vertical, portions thereof areremoved from the recess using anisotropic etching such as reactive ionetching (RIE). That is, the portion of the insulating layer 107 formedon the recess bottom 109 is removed; however the insulating layer formedon the recess sidewalls remains thereon. The end result is that therecess bottom 109 is exposed while the recess sidewalls are conformallycoated with the insulating layer 107. In this illustrative embodiment,the insulating layer 107 is also formed on the interior exposed edges ofthe pad layer, as shown.

In FIG. 3, a buffer layer 113 forms a lattice constant/structuremismatch 121 with the substrate 101 and functions to constrain most ofthe dislocations caused by the mismatch. Illustratively, the bufferlayer may have an overall thickness from less than about 0.5 microns tomore than about 2.0 microns. A relaxed layer 111 is formed on the bufferlayer and remains relatively defect free. Illustratively, the overallthickness of the relaxed layer 111 may be about 0.2 microns. Theseexemplary thickness measurements may be applied to all the embodimentsdescribed herein.

The buffer layer 113 and the relaxed layer 111 are epitaxially grown inthe recess 105, within the confines of the insulating layer 107. Bufferlayer 113 is formed first, then the relaxed layer 111. The buffer layer113 growth process starts from the recess bottom 109 and works upwards,layer after layer, until an overall thickness of approximately 0.5micron to approximately 2.0 micron is reached. In one embodiment,silicon germanium (SiGe) is used to form the buffer layer 113 and therelaxed layer 111 in order to subsequently form a semiconductor layersuch as silicon atop of the relaxed layer 111 with a tensile stress. Inan alternative embodiment, silicon carbon (SiC) may be used to provide acompressive strain in the subsequently formed silicon layer.

The buffer layer 113 and the relaxed layer 111 may be deposited or grownusing conventional techniques such as chemical vapor deposition methods.For example, ultrahigh vacuum chemical vapor deposition (UHVCVD) may beused in a conventional manner to grow a device quality SiGe or SiClayer. Other conventional techniques include rapid thermal chemicalvapor deposition (RTCVD), low pressure chemical vapor deposition(LPCVD), limited reaction processing CVD (LRPCVD) and molecular beamepitaxy (MBE). Optionally, a thin silicon buffer layer (not shown) maybe formed on the interior walls of the recess 105 before SiGe or SiCformation.

The multi-layered buffer layer 113 is constructed in such a fashion thata concentration of a material (Ge, for example) incrementally increasesfrom a base concentration 119 proximate the bottom of the recess to abenchmark concentration 117 proximate a top surface of the buffer layer.This incremental increase in concentration may be in any steppedfashion, such as for example, by 10% for each new deposition or grownlayer. However, any percentage increase may be used depending on thedesired applications and requested costs. In theory, the concentrationof Ge can range from a base concentration of less than about 1% to abenchmark concentration of 100%. However, for cost and other reasons, abenchmark concentration of about 40% may be used. To prevent defectsfrom occurring in the relaxed layer, the second base concentration 115of a material used to form the relaxed layer 111 (i.e., Ge if SiGe isused) is chosen to approximately match the benchmark concentration 117of Ge in the buffer layer 113.

Referring to FIG. 4, the pad layer is removed, and a layer of material(such as, but not limited to, Si) is epitaxially grown within andwithout the confines of the insulating layer 107 to formed relaxedmaterial 123 and strained material 125. Material 123 is described asrelaxed (or non-strained) because its lattice constant approximatelyequals the lattice constant of the substrate 101. Material 125 isdescribed as strained because its lattice constant differs from thelattice constant of a material used to form the relaxed layer 111.Consequently, a lattice mismatch 127 occurs at the interface between thestrained material 125 and the buffer layer 113. Depending on the type ofmaterial used to form the relaxed layer 111, strained material 125 maybe placed in one of a tensile or a compressive state. Illustratively,strained material 125 is tensily strained when it is formed of Si andthe relaxed layer is formed of SiGe. Alternatively, the strainedmaterial 125 is compressively strained when it is formed of Si and therelaxed layer 111 is formed of SiC. However, any two differentsemiconductor materials may be used, because the different latticestructure/constants of each material will exert either a compressive ortensile strain. In one embodiment, the strained material 125 and therelaxed material 123 each have an overall thickness from less than about20 nanometers to more than about 100 nanometers. These exemplarythicknesses may be used in various embodiments herein described.

Referring to FIG. 5, a strained device 129 and a non-strained device 131are formed in the strained material 125 and in relaxed material 123,respectively. Illustratively, strained material 129 is a logic device ora first transistor; and non-strained device 131 is DRAM or a secondtransistor.

Alternate embodiments and methods of manufacture will now be describedwith reference to FIGS. 6-11. Because the materials, etching methods,epitaxial growth methods, and deposition methods used to form theembodiments of FIGS. 6-11 are the same as those described above, thesefigures will be described in less detail in order not to unnecessarilyobscure aspects of the invention.

In FIG. 6, a cross-section of an electrical device 100 is shown. Thedevice 100 includes a substrate 101 covered by a pad layer 103. As shownin FIG. 7, a recess 105 is etched through the pad layer 103 and into thesubstrate 101 to a pre-determined depth, as described above. Thereafter,an oxide or nitride insulating layer 107 is conformally coated on theinterior of the recess 105. The bottom portion of the insulating layer107 is then removed, leaving the portions adhered to the recesssidewalls virtually intact.

FIG. 8 depicts the formation of the buffer layer 113 and the relaxedlayer 111 in the recess 105, within the confines of the insulating layer107. As mentioned above, a material forming the buffer layer varies inconcentration from a base concentration 119 to a benchmark concentration117. A second base concentration 115 of a material forming the relaxedlayer 111 is chosen to approximately match the benchmark concentration117 of the buffer layer 113. As previously disclosed, the buffer layer113 functions to contain dislocations caused by the lattice mismatch121. FIG. 9 illustrates the discrete and selective formation of astrained material 125 in the recess 105, within the confines of theinsulating layer 107, and on top of the relaxed layer 111. As previouslydisclosed, the type of material used to form the relaxed layer 111determines whether a tensile or compressive force is applied to thestrained material 125.

FIG. 10 depicts removal of the pad layer 103 and subsequentplanarization of the substrate 101. This Figure also illustrates thelattice mismatch 127 between the strained material 125 and the relaxedlayer 111. The type of process used to remove the pad layer depends onthe type of material used to form such layers. For example, if siliconnitride is used as the pad layer, then a wet etch using hot phosphoric(H₃PO₄) may be used. The type of planarization method used may be anysuitable planarization technique. For example, in one embodiment,chemical mechanical polishing (CMP) may be used. In another embodiment,a high temperature reflow process with the presence of hydrogen may beused.

FIG. 11 shows the formation of electrical devices 129 and 131 in thestrained material 125 and in the non-strained regions of the substrate101. In this embodiment, portions of the substrate 101 that are outsidethe confines of the insulating layer 107 form the relaxed material 123shown in FIG. 4. As previously described, strained device 129 mayillustratively be, but is not limited to, a logic device or a firsttransistor; non-strained device 131 may illustratively be, but is notlimited to, a DRAM or a second transistor.

A third embodiment is shown with respect to FIGS. 12 16. FIG. 12illustrates a cross-sectional view of an electrical device 100 (i.e., asilicon wafer), which includes a substrate 101 on which are formed, inascending order, buffer layer 113, relaxed layer 111, and strainedmaterial 125. This Figure also illustrates the lattice mismatch 121formed between the substrate 101 and a lower surface of the buffer layer113, and the lattice mismatch 127 formed between the relaxed layer 111and the strained material 125. These layers can be grown or deposited inany known manner, with the buffer layer 113 having, in one embodiment, ahigher concentration of material closest to the strained layer andgradually decreasing in concentration. This will eliminate or reduceformation of defects in the end product.

FIG. 13 depicts the formation of a recess 105 that extends through thepad layer 103, the strained material 125, the relaxed layer 111, and thebuffer layer 113, but which has as its bottom a portion of the topsurface of the substrate 101.

FIG. 14 depicts the formation of insulating layer 107 on the sidewallsof the recess 105. The insulating layer 107 is formed by deposition orgrowth process followed by an etching process, as previously described.FIG. 15 shows a relaxed material (for example, Si) which is selectivelyand epitaxially grown in the recess within the confines of theinsulating material to completely fill the recess. Thereafter, the padlayer is removed, and the substrate is planarized such that the exposedsurfaces of the strained material 125, insulating material, and relaxedmaterial 123 are approximately level. In this embodiment, the strainedmaterial 125 is outside, while the relaxed material 123 is within theconfines of the insulating material 107. That is, the relaxed materialis formed within the recess.

Referring to FIG. 16, there is illustrated the formation of a straineddevice 129 in the strained material 125 and the formation of anon-strained device 131 in the relaxed material 123. As shown, straineddevice 129 is located outside the confines of the insulating material,and the non-strained device is located within those confines.

A fourth embodiment is shown with respect to FIGS. 17 22. Across-sectional view of an electrical device 100 in accordance with thefourth embodiment is shown in FIG. 17. The device 100 includes asubstrate 101 on which a buffer layer 113 of SiGe is formed. In analternate embodiment, SiC can also be formed. A relaxed layer 111, alsoformed of SiGe (or alternatively SiC), covers the top surface of thebuffer layer. The lattice mismatch 121 between the buffer layer and thesilicon substrate 101 is in the illustrative range of 2% or less. Thismeans that the lattice constant of the lowest SiGe buffer layer differsfrom the lattice constant of the silicon substrate by about 2% or less.This same percentage may also be applicable for any of the embodimentsdisclosed herein.

FIG. 18 illustrates the formation of a recess 105 that extends throughthe pad layer 103, through the relaxed layer 111, and through the bufferlayer 113 to expose a top surface of the silicon substrate 101. FIG. 19depicts the formation of an insulating layer 107 on the sidewalls of therecess 105 and the formation of the relaxed material 123 in the recess,as previously described. In FIG. 20, the pad layer has been removed, andthe top surface of relaxed layer 111, insulating layer 107, and relaxedmaterial 123 have been planarized. Thereafter, as shown in FIG. 21, alayer of silicon is epitaxially grown to cover the entire planarizedsurface.

The result of this process is that the lattice mismatch between therelaxed layer and the silicon layer places a tensile or compressivestrain on the silicon, thereby creating strained material 125. Becausethe lattice mismatch between another portion of the silicon layer andthe relaxed material 123 (Si) is negligible, a relaxed (non-strainedmaterial) 124 is created within the confines of the recess 105.Although, in this embodiment, the insulating layer 107 does not separatethe strained material 125 from the second relaxed material 124, thelateral strain between the strained material 125 and non-strainedmaterials 124 is minimal compared to the strain imposed by the strainimposed by the relaxed layer 111.

FIG. 22 illustrates the formation of a strained device 129 in thestrained material 125, and the formation of a non-strained device 131 inthe relaxed material 124. As previously disclosed, the strained device129 may be a logic device, and the non-strained device may be a DRAM.However, other electrical devices, such as transistors and capacitors,may also be used.

FIGS. 23-27 are cross-sectional views of an electrical device 100 thatillustrate the formation of a strained material 125 using doped siliconon a substrate 101. As shown in FIG. 23, a pad layer 103 is formed on asilicon substrate 101. Then, as illustrated by FIG. 24, a recess 105 isetched through the pad layer and into the substrate 101 to an exemplarydepth of approximately 0.05 or 1 microns, as measured from a top surfaceof the substrate 101. Thereafter, an optional insulating layer 107,formed of an oxide or a nitride material, is formed on the sidewalls ofand bottom of the recess 105 using chemical vapor deposition or otherknown processes. Following an etching process to remove the insulatinglayer 107 from the bottom portion of the recess 105, a strained material125 is epitaxially grown in the recess within the confines of theinsulating material 107 until a top surface of the strained materialapproximately matches a top surface of the substrate 101. The strainedlayer 125 has a thickness less than the so-called “critical thickness”.The critical thickness is defined as the maximum thickness of thestrained layer below which virtually no defects are generated.Illustratively, the strained material 125 is carbon-doped silicon.However, other doped semiconductor materials may be used. For example, acompressive-strained layer may be formed by forming a germanium-dopedsilicon layer on silicon substrate.

FIG. 26 shows that the pad layer 103 has been etched away using either adry or wet etch, as previously described, and that the top surface ofthe substrate 101 is planarized to be approximately level with the topsurfaces of strained material 125, insulating layer 107 and thesubstrate 101. In this manner, strained material 125 is selectivelyformed in the recess 105 and separated from the non-strained areas 126of the substrate 101 by the insulating layer 107. As shown in FIG. 27, astrained device 129, such as a logic device, is formed in the strainedmaterial 125; and a non-strained device 131 is formed in the nonstrained area 126 of the substrate 101.

FIGS. 28-32 are cross-sectional views of an electrical device 100 thatillustrate another formation of a strained material 125 using dopedsilicon on a silicon substrate 101. In FIG. 28, a silicon substrate 101is prepared for processing. In FIG. 29, a carbon-doped strained material125 is epitaxially grown on a top surface of the substrate 101. Thestrained layer 125 has a thickness less than the so-called “criticalthickness”. The critical thickness is defined as the maximum thick ofthe strained layer below which there is virtually no defects isgenerated. Illustratively, the strained material 125 is carbon-dopedsilicon. However, other doped semiconductor materials may be used. Forexample, a compressive-strained layer may be formed by forming agermanium-doped silicon layer on silicon substrate.

In FIG. 30, a patterned pad layer 103 is formed on the strained material125. Areas of the non-strained silicon substrate are exposed by using anetching process to remove areas of strained doped material 125 that arenot covered by the pad layer 103.

In FIG. 31, a non-strained (relaxed) material 123 is epitaxially grownon the exposed areas of the substrate 101 to approximately the sameheight of the strained layer 125 to form a substantially planar topsurface. Epitaxially growing the non-strained material 123 is optional,since the strained material 125, in this embodiment, is very thin (e.g.,less than about 100 nanometers). Thereafter, as shown in FIG. 32, thepad layer 103 is etched away and a strained device 129 is formed in thestrained material 125. A non-strained device 131 is formed in therelaxed material 123. Alternatively, if a relaxed material 123 is notused, the non-strained device 131 is formed in a non-strained area ofthe substrate 101. Again, permitting the strained material 125 tocontact the adjacent relaxed material 123 usually does not pose problemsbecause the lateral strain experienced by both materials issignificantly less than the strain created by the doped semiconductormaterial that forms the strained material 125. Illustratively, thestrained material 125 is carbon-doped silicon. However, other dopedsemiconductor materials may be used. For example, a compressive-strainedlayer may be formed by forming a germanium-doped silicon layer onsilicon substrate.

FIG. 33 is a cross-sectional view illustrating an electrical device 100having tensile-strained, compressive-strained, and non-strainedmaterials 123, 124, and 123, respectively. As shown, each of thesematerials is formed on a surface of a substrate 101 using anycombination of the techniques discussed above. The lateral strainexperienced at junctions 133 is minimal compared to the vertical strainexerted by the lattice mismatches 127A and 127B, respectively.Alternatively, these layers may also be separated by insulatingmaterials. In one embodiment, the tensile strained material 125A is acarbon-doped silicon layer formed on silicon and the compressivestrained material 125B is a germanium-doped silicon layer formed onsilicon. Alternatively, the tensile strained material 125A is a siliconlayer formed on the SiGe buffer layer(s) (not shown) and the compressivestrained material 125B is a silicon layer formed on SiC buffer layer(s)(not shown). Although illustratively shown as a layer, the relaxedmaterial 123 may also be a relaxed top surface of the substrate 101, aspreviously illustrated and described with reference to FIGS. 31 and 32.Although illustratively shown that these layers have the same thickness,their thicknesses may not necessary be the same.

It should be understood that FIGS. 1-33 can equally represent methods ofmanufacture. In any event, FIGS. 34-39 show various methods formanufacturing the apparatus according to various aspects of theinvention. Although herein described with reference to sequentialreference numerals, the steps of each method may be performed in anyorder. The removing of layers to form a recess, forming layers and otherprocesses may be provided by any known method of fabrication. Forexample, illustrative manufacturing processes include, but are notlimited to, chemical vapor deposition, ultra-high vacuum chemical vapordeposition, and reactive ion etching (RIE), electrolytic etching, plasmaetching, dry etching, and the like. Ion etching is a process of removingunwanted material by selectively bombarding an area or areas of a solidor liquid substance with energetic ionized particles. Often used in themanufacture of microelectronics, plasma etching creates reactive speciesin a plasma and then uses the reactive species to selectively removeunwanted material.

FIG. 34 is a flowchart illustrating an exemplary method of manufacturingan electrical device 100, according to one embodiment of the invention.At step 3401, a recess is patterned and formed in a substrate covered bya pad layer. At step 3403, an insulating layer is optionally formed onthe sidewalls and bottom of the recess. At step 3405, a portion of theinsulating layer is removed from the bottom of the recess to expose aportion of the substrate. At step 3407, a buffer layer is formed in therecess within the confines of the insulating layer, the buffer layerhaving a lattice constant/structure mismatch with the substrate. At step3409 the concentration of a material forming the buffer layer isincreased as the buffer layer is formed from a base concentration to abenchmark concentration. At step 3411, a relaxed layer is formed on thebuffer layer. At step 3413, the pad layer is stripped. At step 3415, astrained material is formed on the relaxed layer within the confines ofthe insulating layer, and a non-strained material is formed on a portionof the substrate outside the confines of the insulating layer. At step3417 a strained device is formed in the strained material. At step 3419a non-strained device is formed in the relaxed material. In oneembodiment, a material forming the relaxed layer has a second baseconcentration proximate a bottom surface thereof that approximatelyequals the benchmark concentration proximate a top surface of the bufferlayer.

FIG. 35 is a flowchart illustrating an exemplary method of manufacturingan electrical device 100, according to one embodiment of the invention.At step 3501 a recess is patterned and formed in a substrate covered bya pad layer. At step 3503 an insulating layer is formed on the sidewallsand bottom of the recess. At step 3505, a portion of the insulatinglayer is removed from the bottom of the recess to expose a portion ofthe substrate. At step 3507, a buffer layer is formed in the recesswithin the confines of the insulating layer, the buffer layer having alattice constant/structure mismatch with the substrate. At step 3509,the concentration of a material forming the buffer layer is increased asthe buffer layer is formed, from a base concentration to a benchmarkconcentration. At step 3511 a relaxed layer is formed on the bufferlayer. At step 3513 a strained material is formed on the relaxed layerin the recess within the confines of the insulating layer. At step 3515,the pad layer is stripped. At step 3517 the substrate is planarized. Atstep 3519 a strained device is formed in the strained material. At step3521 a non-strained device is formed in the relaxed material. In oneembodiment, a material forming the relaxed layer has a second baseconcentration proximate a bottom surface thereof that approximatelyequals the benchmark concentration proximate a top surface of the bufferlayer.

FIG. 36 is a flowchart illustrating an exemplary method of manufacturingan electrical device 100, according to one embodiment of the invention.At step 3601 a pad layer is formed on a strained material. At step 3603,a recess is patterned and formed through the strained material, througha relaxed layer previously formed proximate thereto, and through abuffer layer previously formed proximate to the relaxed layer and incontact with a substrate. At step 3605 an insulating layer is formed onthe sidewalls and bottom of the recess. At step 3607 the insulatinglayer is removed from the bottom of the recess. At step 3609, a relaxedmaterial is formed in the recess within the confines of the insulatingmaterial. At step 3611, the pad layer is stripped. At step 3613, thesubstrate is planarized. At step 3615, a strained device is formed inthe strained material. At step 3617 a non-strained device is formed inthe relaxed material.

FIG. 37 is a flowchart illustrating an exemplary method of manufacturingan electrical device 100, according to one embodiment of the invention.At step 3701 a pad layer is patterned and formed on a relaxed layerpreviously formed on a buffer layer, the buffer layer being previouslyformed on a substrate. At step 3703 a recess is formed through therelaxed layer and the buffer layer. At step 3705 an insulating layer isformed on the sidewalls and bottom of the recess. At step 3707 a portionof the insulating layer is removed from the bottom of the recess toexpose a portion of the substrate. At step 3709 a relaxed material inthe recess within the confines of the insulating material. At step 3711the pad layer is stripped. At step 3713 the substrate is planarized. Atstep 3715 a strained material is formed on the relaxed layer outside theconfines of the insulating layer. At step 3717, a relaxed material isformed in the recess within the confines of the insulating layer. Atstep 3719, a strained device is formed in the strained material. At step3721, a non-strained device is formed in the relaxed material.

FIG. 38 is a flowchart illustrating an exemplary method of manufacturingan electrical device 100, according to one embodiment of the invention.At step 3801 a recess is patterned and formed in a substrate covered bya pad layer. At step 3803 an insulating layer is formed on the sidewallsand bottom of the recess. At step 3805 a portion of the insulating layerfrom the bottom of the recess to expose a portion of the substrate. Atstep 3807 a strained material is selectively and epitaxially grown inthe recess within the confines of the insulating layer. At step 3809,the pad layer is stripped. At step 3811, a strained device is formed inthe strained material. At step 3813 a non-strained device is formed in arelaxed area of the substrate outside the confines of the insulatinglayer. In this embodiment, the strained material may be a carbon-dopedmaterial, such as, but not limited to, carbon-doped silicon.Alternatively, the strained material may be a germanium-doped material,such as, not limited to, germanium-doped silicon.

FIG. 39 is a flowchart illustrating an exemplary method of manufacturingan electrical device 100, according to one embodiment of the invention.At step 3901 a strained material is formed on a substrate. At step 3903a pad layer is formed on the strained material. At step 3905, selectiveareas of the strained material are removed to expose correspondingportions of the substrate. At step 3907 a relaxed material is optionallygrown on the exposed substrate to approximately the same height as thestrained layer. At step 3909 the pad layer is stripped. At step 3911 astrained device is formed in the strained material. At step 3913 anon-strained device is formed in the relaxed material. In thisembodiment, the strained material may be a carbon-doped material, suchas, but not limited to, carbon-doped silicon.

Although embodiments of the invention have been illustrated in FIGS.1-22 as fusing SiGe to form a tensile-strained material 125, it will beappreciated that other materials, such as SiC, may be substituted forSiGe, where it is desired to form a compressive-strained material 125.Additionally, a tensile-strained material 125 may be formed byepitaxially growing carbon-doped silicon on a silicon substrate. Othermaterials such as gallium phosphorus, gallium arsenic and the like, mayalso be substituted for SiGe, depending on desired applications andrequested costs. As herein described, an electrical device formed inaccordance with an embodiment of the invention may have a non-strained(relaxed) material 123, 124, 126 patterned proximate a strained material125, 125A and 125B, as illustratively shown and described with respectto FIGS. 4, 15, 21, 26, 31 and 33.

While some exemplary embodiments of this invention have been describedin detail, those skilled in the art will recognize that there are manypossible modifications and variations which may be made in theseexemplary embodiments while yet retaining many of the novel features andadvantages of the invention.

1. An electrical device, comprising: a pattern of strained material andrelaxed material formed on a substrate; a buffer layer formed on thesubstrate and having a lattice constant/structure mismatch with thesubstrate; and a relaxed layer formed on the buffer layer, a top surfaceof the relaxed layer placing the strained material in one of a tensileor a compressive state, wherein the relaxed layer comprises a materialwhich has a lattice constant/structure mismatch with the strainedmaterial; and wherein a material forming the buffer layer increases inconcentration from a base concentration proximate the substrate to abenchmark concentration proximate the relaxed layer.
 2. The electricaldevice of claim 1, further comprising a recess formed in the substrateand enclosing the buffer layer, the recess having sidewalls.
 3. Theelectrical device of claim 2, further comprising an insulating layerformed on the sidewalls.
 4. The electrical device of claim 3, wherein amaterial that forms the insulating layer is one of an oxide and anitride.
 5. The electrical device of claim 3, wherein a portion of thesubstrate forms the relaxed material and is located outside a confine ofthe insulating material.
 6. The electrical device of claim 3, whereinthe relaxed material is formed in the recess within a confine of theinsulating layer.
 7. The electrical device of claim 6, wherein therelaxed layer and the buffer layer are selected from the groupconsisting of silicon carbon (SiC), silicon germanium (SiGe),Al_(X1)Ga_(X2)In_(X3)As_(Y1)P_(Y2)N_(Y3)Sb₄, where X1, X2, X3, Y1, Y2,Y3, and Y4 represent relative proportions, each greater than or equal tozero and X1+X2+X3+Y1+Y2+Y3+Y4=1, and Zn_(A1)Cd_(A2)Se_(B1)Te_(B2), whereA1, A2, B1, and B2 are relative proportions each greater than or equalto zero and A1+A2+B1+B2=1.
 8. The electrical device of claim 1, whereinthe relaxed layer and the buffer layer are selected from the groupconsisting of silicon carbon (SiC), silicon germanium (SiGe),Al_(X1)Ga_(X2)In_(X3)As_(Y1)P_(Y2)N_(Y3)Sb_(Y4), where X1, X2, X3, Y1,Y2, Y3, and Y4 represent relative proportions, each greater than orequal to zero and X1+X2+X3+Y1+Y2+Y3+Y4=1, andZn_(A1)Cd_(A2)Se_(B1)Te_(B2), where A1, A2, B1, and B2 are relativeproportions each greater than or equal to zero and A1+A2+B1+B2=1.
 9. Theelectrical device of claim 1, wherein a material forming the relaxedlayer has a second base concentration proximate the buffer layer thatapproximately equals the benchmark concentration.
 10. The electricaldevice of claim 1, further comprising: a strained device formed in thestrained material; and a non-strained device formed in the relaxedmaterial.
 11. The electrical device of claim 10, wherein thenon-strained device is formed directly on the substrate.
 12. Theelectrical device of claim 1, wherein the strained material comprises agermanium-doped silicon layer formed on and contacting the substrate.13. The electrical device of claim 1, wherein: the base concentration isat a bottom of the buffer layer; and the benchmark concentration is at atop of the buffer layer.
 14. The electrical device of claim 13, whereinthe relaxed layer has a second base concentration at a bottom of therelaxed layer that approximately equals the benchmark concentration atthe top of the buffer layer.
 15. The electrical device of claim 14,wherein the relaxed layer comprises a material which has a latticeconstant/structure mismatch with the strained material.
 16. Theelectrical device of claim 15, wherein the buffer layer comprisesmultiple layers wherein each respective one of the layers has adifferent concentration of a material such that the concentration of thematerial in the buffer layer incrementally increases from the baseconcentration proximate the substrate to the benchmark concentrationproximate the top of the buffer layer.